THE effects of continuing to work during the late stages of pregnancy are equal to those of smoking, a new study carried out at the University of Essex has revealed.

Research showed that women who worked after they were eight months’ pregnant had babies which were on average around half a pound lighter than those who stopped work between six and eight months.

The birth weight of babies born to mothers under the age of 24 was not affected by them continuing to work, but in older mothers the effect was more significant.

The study, which drew on data from three major studies, two in the UK and one in the USA, found the effect of continuing to work during the late stages of pregnancy was equal to that of smoking while pregnant.

Past research has shown babies with low birth weights are at higher risks of poor health and slow development, and may suffer from multiple problems later in life.

Stopping work early in pregnancy was particularly beneficial for women with lower levels of education, the study found – suggesting that the effect of working during pregnancy was possibly more marked for those doing physically-demanding work.

The research was conducted by three economists, Marco Francesconi, Emilia Del Bono and John Ermisch of the the Institute of Social and Economic Research at the University of Essex.

Professor Francesconi said the Government should consider introducing incentives for employers to offer more flexible maternity leave to women who might need a break before, rather than after, their babies were born.

Babies with low birth weights tended to cost the state more money later on, he said.

“We know low birth weight is a predictor of many things that happen later, including lower chances of completing school successfully, lower wages, and higher mortality,” he said. “We need to think seriously about parental leave, because – as this study suggests – the possible benefits of taking leave flexibly before the birth could be quite high.”

The findings are included in a paper titled Intrafamily Resource Allocations: A Dynamic Structural Model of Birth Weight. The paper is included in the July edition of the Journal of Labor Economics, published by the University of Chicago.

The researchers identified 912 children whose mothers were part of the British Household Panel Survey, a longitudinal study conducted between 1991 and 2005, and for whom data was available.

A further sample of 17,483 women who gave birth in 2000 or 2001 and who took part in the Millennium Cohort Study was also examined and showed similar results, along with 12,166 from the National Survey of Family Growth, relating to births in the USA between the early 1970s and 1995.